Tonight is my first attempt at an over night cook. I have a 12 butt that I put on a 7 p.m.. BGE stabilized at 220. When I first put my temp. gauges in they registered 51 degrees F. Now after 2 1/2 hours it is already up to 130. I thought this was going to take 18 hours or so. Is this normal? I am ready to go to bed, if this is the way it should be, thanks for any help.